Neotropical Hydrangeaceae

Daniela Zappi

Royal Botanic Gardens, Kew, UK. 

Description

Shrubs, vines and lianas. Leaves simple, opposite, stipules absent, entire, margins often crenate or serreate, stellate hairs often present. Inflorescence terminal or axillary, cymose, in Hydrangea with sterile flowers at tips of outer branches. Flowers showy or small, hermaphrodite, actinomorphic; sepals 4-5, united forming a short tube; petals 4-5, free, white, or pink, sometimes with purple blotch at base in Philadelphus; stamens (4-)5-10 or >15, free, anthers 2-locular; ovary inferior, 2-4 carpellate, incompletely bi-locular, styles fused in Philadelphus, separate in Hydrangea and Deutzia, placentation axile and or parietal, ovules many.  Fruit capsular, variously dehiscent, many seeded; seeds small, testa reticulate.

Notes on delimitation

  • Recent studies place this family close to the Cornaceae (APG II, 2003) in order Cornales.

Distribution in the Neotropics

  • In the Neotropics the Hydrangeaceae is a marginal family with a few genera ocurring at high altitude and reaching Mexico from the West of the USA, and only Hydrangea (Hydrangea peruviana Moric. ex Ser.) reaching Peru and Chile. Apart from cultivated species, this family is absent from Brazil.

Distinguishing characters (always present)

Other important characters

  • Stellate hairs.
  • Sterile flowers at the edge of inflorescences.
  • Stamens often twice as many as petals or more.

Key differences from similar families

  • The opposite leaves and inferior ovary might cause confusion with families included in the Gentianales (Rubiaceae and others), Caprifoliaceae, Lamiales. The free petals and stamens twice as many as petals found in Hydrangeaceae are good characters to separate them.

Number of genera

  • Deutzia Thunb. - Temperate Asia and North America south to Mexico, 2 - 3 species.
  • Hydrangea L. - Temperate Asia, reaching Mexico, 5 - 10 species.
  • Philadelphus L. - Temperate Asia and North America, reaching Mexico, 5 - 6 species.

Useful tips for generic identification

Key to genera of Neotropical Hydrangeaceae

1. Inflorescences in large terminal corymbs often with sterile outer flowers ... Hydrangea
1. Inflorescences smaller, axillary, flowers all fertile ... 2

2. Flowers pentamerous, petals 5 ... Deutzia
2. Flowers tetramerous, petals 4 ... Philadelphus

Status

  • Many cultivars of Hydrangea are popular plants in cooler climates in South America. The family as a whole is not a very expressive family in the region, with only a few species ocurring only marginally in the area.

Important literature

APG II, 2003. An update of the Angiosperm Phylogeny group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141(4): 399-436.

Hufford, L. Hydrangeaceae. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds.). Flowering Plants of the Neotropics, p. 188-1889.  The New York Botanical Garden, Princeton University Press, Princeton.

How to cite

Zappi, D. (2009). Neotropical Hydrangeaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Hydrangeaceae.htm.